UWSP Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the UWSP Observatory clear sky chart from 2005-11-06 to 2026-04-02.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.

Observation Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(no limit)	Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

By Month

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

		Occurrence of each Forecast	Data Points
Cloud Cover	Day	13% 9% 3 8% 5% 4 4 4 5% 7% 38%	131604
	Night	13% 10% 4 9% 5% 4 4 3 5% 6% 38%	130538
Transparency	Day	45% 5% 12% 25% 13% 1	135051
	Night	47% 5% 11% 23% 13% 1	135152
Seeing	Day	17% 11% 30% 25% 13% 4	17840
	Night	17% 10% 31% 30% 10% 1	27871

By Month

Percentage Cloud Cover SE (2006-)
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	10% 12% 6% 15% 7% 6% 5% 3 4 5% 27%	4691
	11th to 20th	Day	7% 14% 7% 13% 5% 5% 6% 7% 6% 7% 24%	4710
	21st to end	Day	8% 11% 5% 12% 5% 5% 5% 3 5% 7% 34%	5276
February	1st to 10th	Day	9% 11% 6% 9% 6% 5% 5% 5% 6% 7% 31%	1890
	11th to 20th	Day	10% 11% 3 9% 6% 4 5% 4 6% 6% 36%	1933
	21st to end	Day	10% 13% 5% 11% 5% 5% 5% 4 4 8% 30%	1730
March	1st to 10th	Day	13% 8% 2 5% 3 3 4 3 5% 7% 48%	4580
	11th to 20th	Day	11% 8% 3 7% 5% 5% 4 4 6% 8% 40%	4935
	21st to end	Day	24% 11% 4 9% 4 4 4 3 4 5% 29%	6019
April	1st to 10th	Day	16% 13% 4 7% 5% 4 5% 3 5% 7% 31%	2412
	11th to 20th	Day	20% 10% 3 7% 5% 4 4 3 5% 5% 33%	2374
	21st to end	Day	19% 11% 3 7% 6% 5% 5% 3 4 6% 31%	2495
May	1st to 10th	Day	15% 6% 3 6% 4 3 4 3 5% 6% 46%	6224
	11th to 20th	Day	14% 6% 2 7% 4 4 4 3 6% 7% 42%	6319
	21st to end	Day	17% 7% 2 7% 5% 4 4 4 5% 6% 39%	6935
June	1st to 10th	Day	13% 6% 2 6% 5% 4 4 3 5% 9% 44%	2800
	11th to 20th	Day	16% 6% 2 7% 4 4 5% 4 6% 8% 37%	2800
	21st to end	Day	13% 6% 2 6% 5% 5% 5% 4 7% 9% 39%	2800
July	1st to 10th	Day	11% 5% 2 6% 4 5% 5% 5% 7% 10% 42%	6360
	11th to 20th	Day	7% 3 2 5% 4 4 5% 4 7% 10% 50%	6360
	21st to end	Day	10% 6% 3 7% 4 4 5% 4 6% 8% 44%	6924
August	1st to 10th	Day	11% 6% 2 7% 4 5% 6% 4 6% 8% 41%	4563
	11th to 20th	Day	14% 5% 2 5% 4 4 5% 3 6% 8% 45%	4026
	21st to end	Day	12% 6% 2 8% 4 4 5% 4 5% 8% 41%	4312
September	1st to 10th	Day	14% 6% 2 5% 4 4 4 4 6% 7% 45%	2400
	11th to 20th	Day	13% 5% 2 6% 3 5% 4 4 5% 7% 46%	2347
	21st to end	Day	14% 7% 2 7% 3 5% 5% 4 6% 7% 40%	2200
October	1st to 10th	Day	13% 7% 2 7% 5% 4 3 4 5% 7% 44%	2018
	11th to 20th	Day	18% 13% 3 8% 4 4 4 3 4 7% 32%	2000
	21st to end	Day	17% 11% 4 7% 4 3 4 4 4 6% 36%	1994
November	1st to 10th	Day	14% 9% 3 6% 5% 4 3 3 5% 7% 41%	1852
	11th to 20th	Day	14% 13% 4 10% 6% 5% 4 4 6% 5% 30%	1797
	21st to end	Day	16% 11% 4 9% 5% 5% 4 3 5% 6% 33%	1680
December	1st to 10th	Day	7% 10% 6% 15% 7% 6% 6% 4 5% 5% 27%	2690
	11th to 20th	Day	11% 17% 7% 12% 6% 5% 3 3 4 5% 28%	3088
	21st to end	Day	19% 20% 7% 14% 5% 4 3 3 4 3 17%	4070
January	1st to 10th	Night	11% 13% 6% 13% 7% 4 3 2 3 4 34%	8232
	11th to 20th	Night	8% 14% 6% 14% 7% 5% 7% 5% 5% 5% 23%	8280
	21st to end	Night	7% 13% 7% 11% 6% 5% 6% 4 5% 6% 31%	8923
February	1st to 10th	Night	9% 12% 5% 11% 5% 5% 3 4 6% 5% 33%	2730
	11th to 20th	Night	10% 9% 4 9% 5% 5% 5% 4 4 6% 39%	2572
	21st to end	Night	14% 11% 4 9% 6% 4 5% 4 4 6% 32%	2076
March	1st to 10th	Night	12% 7% 2 7% 4 4 4 4 4 6% 46%	5493
	11th to 20th	Night	10% 10% 3 8% 5% 5% 5% 4 5% 7% 38%	5289
	21st to end	Night	23% 10% 3 9% 5% 4 4 3 4 6% 30%	5151
April	1st to 10th	Night	19% 11% 3 7% 4 4 3 3 5% 5% 36%	2010
	11th to 20th	Night	21% 7% 3 6% 5% 3 4 3 6% 5% 37%	1975
	21st to end	Night	18% 9% 2 7% 4 4 5% 4 5% 6% 37%	1904
May	1st to 10th	Night	15% 8% 3 6% 4 4 4 3 4 6% 43%	3683
	11th to 20th	Night	11% 5% 2 6% 4 4 4 4 6% 7% 47%	3596
	21st to end	Night	17% 9% 3 7% 4 4 4 3 5% 6% 40%	3942
June	1st to 10th	Night	11% 5% 2 5% 4 5% 5% 4 6% 7% 45%	1600
	11th to 20th	Night	12% 6% 3 7% 5% 4 5% 4 6% 8% 39%	1600
	21st to end	Night	12% 5% 2 5% 5% 4 4 4 5% 7% 47%	1600
July	1st to 10th	Night	13% 4 2 6% 5% 4 5% 4 6% 9% 43%	3618
	11th to 20th	Night	10% 4 2 4 3 3 3 4 6% 8% 54%	3617
	21st to end	Night	7% 5% 2 6% 4 4 4 4 5% 8% 51%	3947
August	1st to 10th	Night	11% 5% 2 6% 4 4 4 3 5% 7% 48%	2597
	11th to 20th	Night	11% 6% 2 6% 4 4 4 3 5% 7% 47%	3026
	21st to end	Night	11% 5% 2 5% 4 4 5% 3 6% 6% 47%	3586
September	1st to 10th	Night	10% 5% 2 4 3 3 4 3 5% 7% 53%	2000
	11th to 20th	Night	12% 5% 2 4 3 3 4 3 5% 7% 52%	2032
	21st to end	Night	12% 6% 2 6% 3 3 4 3 4 7% 49%	2200
October	1st to 10th	Night	12% 6% 3 5% 3 3 5% 3 5% 6% 49%	2380
	11th to 20th	Night	16% 9% 3 7% 4 4 4 4 5% 7% 38%	2400
	21st to end	Night	17% 12% 3 7% 4 4 4 3 4 6% 34%	2845
November	1st to 10th	Night	15% 9% 3 6% 4 4 3 3 5% 5% 43%	2666
	11th to 20th	Night	13% 13% 4 9% 5% 5% 5% 3 4 5% 35%	2819
	21st to end	Night	14% 13% 4 9% 5% 4 4 3 4 5% 34%	2940
December	1st to 10th	Night	9% 10% 4 11% 5% 5% 5% 4 6% 8% 33%	4720
	11th to 20th	Night	13% 17% 6% 13% 5% 4 4 3 4 4 26%	5339
	21st to end	Night	23% 15% 6% 11% 4 4 3 3 4 5% 23%	7150

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	61% 3 11% 16% 8%	4692
	11th to 20th	Day	58% 5% 7% 17% 12% 1	4710
	21st to end	Day	51% 3 9% 24% 12%	5276
February	1st to 10th	Day	51% 5% 14% 18% 11% 1	1890
	11th to 20th	Day	46% 6% 11% 24% 11% 1	1942
	21st to end	Day	52% 7% 12% 19% 9% 2	1730
March	1st to 10th	Day	38% 3 12% 24% 17% 5%	4580
	11th to 20th	Day	40% 4 16% 23% 14% 2	4935
	21st to end	Day	58% 4 8% 16% 12% 1	6021
April	1st to 10th	Day	52% 7% 10% 19% 11% 1	2412
	11th to 20th	Day	52% 6% 8% 21% 11% 2	2374
	21st to end	Day	53% 7% 10% 18% 11% 1	2495
May	1st to 10th	Day	38% 6% 11% 28% 15% 2	6261
	11th to 20th	Day	40% 5% 12% 27% 15% 1	6323
	21st to end	Day	45% 5% 9% 24% 15% 1	6949
June	1st to 10th	Day	37% 6% 13% 28% 14% 1	2800
	11th to 20th	Day	43% 7% 13% 24% 12% 1	2800
	21st to end	Day	40% 8% 15% 25% 12% 1	2800
July	1st to 10th	Day	38% 4 16% 34% 7% 1	6291
	11th to 20th	Day	30% 4 15% 36% 14% 1	6285
	21st to end	Day	39% 4 13% 26% 17% 1	6728
August	1st to 10th	Day	41% 5% 14% 25% 13% 1	4548
	11th to 20th	Day	37% 5% 12% 34% 12%	4065
	21st to end	Day	42% 3 13% 30% 11% 1	4311
September	1st to 10th	Day	38% 6% 13% 27% 15% 1	2400
	11th to 20th	Day	36% 7% 16% 31% 9% 1	2347
	21st to end	Day	41% 7% 12% 27% 12%	2200
October	1st to 10th	Day	27% 4 8% 39% 23%	3278
	11th to 20th	Day	44% 4 10% 25% 15% 1	3240
	21st to end	Day	45% 3 13% 29% 10%	3194
November	1st to 10th	Day	43% 5% 13% 23% 15% 1	1852
	11th to 20th	Day	55% 5% 11% 20% 9% 1	1797
	21st to end	Day	53% 5% 15% 21% 5% 1	1680
December	1st to 10th	Day	58% 5% 11% 20% 5% 1	2690
	11th to 20th	Day	59% 5% 9% 16% 11% 1	3085
	21st to end	Day	72% 4 6% 12% 6%	4070
January	1st to 10th	Night	56% 3 9% 21% 11%	8233
	11th to 20th	Night	62% 5% 7% 12% 13% 1	8280
	21st to end	Night	55% 4 9% 17% 14%	8923
February	1st to 10th	Night	51% 5% 10% 22% 11% 1	2730
	11th to 20th	Night	45% 7% 10% 24% 11% 2	2573
	21st to end	Night	52% 6% 11% 19% 10% 2	2076
March	1st to 10th	Night	39% 4 14% 25% 13% 5%	5493
	11th to 20th	Night	44% 5% 15% 21% 12% 2	5289
	21st to end	Night	56% 5% 9% 18% 12% 1	5151
April	1st to 10th	Night	50% 5% 8% 19% 17% 1	2010
	11th to 20th	Night	47% 6% 10% 21% 13% 3	1975
	21st to end	Night	44% 7% 12% 21% 14% 1	1904
May	1st to 10th	Night	42% 6% 11% 19% 18% 4	3708
	11th to 20th	Night	34% 7% 13% 26% 18% 2	3597
	21st to end	Night	45% 6% 10% 24% 14% 1	3950
June	1st to 10th	Night	33% 9% 14% 27% 16% 1	1600
	11th to 20th	Night	41% 7% 13% 23% 14% 2	1600
	21st to end	Night	35% 6% 15% 28% 12% 3	1600
July	1st to 10th	Night	38% 3 17% 30% 10% 2	3580
	11th to 20th	Night	30% 4 15% 34% 16% 1	3572
	21st to end	Night	33% 4 15% 26% 20% 2	3832
August	1st to 10th	Night	36% 5% 13% 28% 16% 1	2588
	11th to 20th	Night	37% 5% 12% 30% 14% 1	3053
	21st to end	Night	37% 4 14% 25% 18% 2	3586
September	1st to 10th	Night	30% 6% 12% 31% 19% 1	2000
	11th to 20th	Night	33% 6% 13% 34% 14% 1	2032
	21st to end	Night	35% 5% 12% 31% 16% 1	2200
October	1st to 10th	Night	28% 4 7% 37% 22% 3	3887
	11th to 20th	Night	35% 4 10% 33% 18% 1	3899
	21st to end	Night	49% 3 9% 23% 15%	4595
November	1st to 10th	Night	42% 5% 12% 25% 15% 1	2666
	11th to 20th	Night	52% 5% 12% 18% 11% 2	2819
	21st to end	Night	51% 5% 13% 23% 7% 1	2940
December	1st to 10th	Night	50% 5% 18% 21% 5% 2	4720
	11th to 20th	Night	62% 4 8% 15% 10% 1	5341
	21st to end	Night	65% 4 7% 15% 9%	7150

Seeing (when cloud cover <= 80%)
Color Meanings: Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	15% 15% 34% 25% 9% 2	330
	11th to 20th	Day	20% 14% 38% 22% 6% 1	330
	21st to end	Day	19% 15% 36% 25% 5%	363
February	1st to 10th	Day	15% 17% 41% 20% 6% 2	330
	11th to 20th	Day	17% 20% 37% 18% 7%	330
	21st to end	Day	19% 16% 44% 19% 1	273
March	1st to 10th	Day	19% 14% 41% 21% 5%	330
	11th to 20th	Day	24% 14% 34% 20% 7% 2	330
	21st to end	Day	27% 12% 32% 22% 6% 1	553
April	1st to 10th	Day	27% 16% 30% 23% 3	504
	11th to 20th	Day	29% 14% 26% 19% 9% 2	492
	21st to end	Day	22% 14% 34% 19% 10% 2	500
May	1st to 10th	Day	20% 12% 31% 28% 8% 1	659
	11th to 20th	Day	19% 11% 29% 24% 13% 4	725
	21st to end	Day	20% 9% 28% 26% 12% 5%	789
June	1st to 10th	Day	13% 9% 29% 30% 14% 5%	730
	11th to 20th	Day	19% 8% 30% 26% 13% 4	730
	21st to end	Day	16% 8% 29% 29% 13% 4	730
July	1st to 10th	Day	8% 3 22% 33% 25% 9%	721
	11th to 20th	Day	8% 6% 26% 35% 16% 8%	718
	21st to end	Day	7% 3 27% 32% 22% 8%	794
August	1st to 10th	Day	11% 5% 23% 29% 23% 9%	726
	11th to 20th	Day	13% 5% 22% 26% 24% 10%	626
	21st to end	Day	14% 6% 21% 30% 21% 8%	583
September	1st to 10th	Day	15% 8% 23% 27% 18% 7%	530
	11th to 20th	Day	13% 5% 20% 37% 20% 5%	530
	21st to end	Day	17% 10% 25% 27% 18% 4	530
October	1st to 10th	Day	15% 13% 28% 25% 15% 4	348
	11th to 20th	Day	24% 15% 36% 18% 7%	330
	21st to end	Day	22% 15% 36% 22% 4 2	363
November	1st to 10th	Day	19% 15% 37% 20% 8% 1	330
	11th to 20th	Day	19% 20% 34% 22% 5%	330
	21st to end	Day	23% 15% 42% 14% 6%	330
December	1st to 10th	Day	16% 15% 44% 18% 7%	330
	11th to 20th	Day	19% 22% 38% 17% 4 1	330
	21st to end	Day	28% 17% 35% 15% 5% 1	363
January	1st to 10th	Night	17% 13% 38% 26% 6% 1	1050
	11th to 20th	Night	18% 14% 36% 26% 6% 1	1050
	21st to end	Night	18% 10% 37% 28% 6%	1155
February	1st to 10th	Night	16% 13% 37% 29% 6%	1050
	11th to 20th	Night	16% 14% 37% 26% 7%	938
	21st to end	Night	20% 15% 36% 25% 4	692
March	1st to 10th	Night	17% 14% 34% 28% 7% 1	840
	11th to 20th	Night	20% 12% 35% 24% 8%	725
	21st to end	Night	19% 11% 30% 31% 7% 2	693
April	1st to 10th	Night	23% 11% 35% 24% 6%	603
	11th to 20th	Night	23% 10% 32% 28% 7%	593
	21st to end	Night	22% 10% 32% 29% 6% 1	600
May	1st to 10th	Night	22% 8% 36% 28% 6% 1	600
	11th to 20th	Night	19% 9% 31% 31% 9% 1	591
	21st to end	Night	16% 6% 23% 41% 14%	650
June	1st to 10th	Night	13% 6% 29% 39% 13% 1	600
	11th to 20th	Night	15% 5% 32% 36% 11% 1	600
	21st to end	Night	12% 5% 25% 43% 14% 1	600
July	1st to 10th	Night	9% 2 20% 44% 24% 2	585
	11th to 20th	Night	9% 3 22% 43% 20% 3	582
	21st to end	Night	7% 3 19% 47% 22% 2	657
August	1st to 10th	Night	9% 3 17% 46% 24% 2	597
	11th to 20th	Night	12% 3 18% 37% 27% 3	594
	21st to end	Night	13% 3 20% 42% 19% 3	660
September	1st to 10th	Night	13% 4 24% 37% 18% 5%	600
	11th to 20th	Night	13% 4 25% 35% 20% 3	632
	21st to end	Night	15% 7% 24% 37% 17% 1	800
October	1st to 10th	Night	15% 8% 27% 30% 18% 1	800
	11th to 20th	Night	19% 12% 33% 29% 7%	800
	21st to end	Night	23% 11% 31% 27% 8%	880
November	1st to 10th	Night	19% 10% 36% 25% 8% 1	820
	11th to 20th	Night	20% 15% 36% 22% 7%	929
	21st to end	Night	22% 15% 35% 22% 5%	1050
December	1st to 10th	Night	20% 12% 38% 23% 6%	1050
	11th to 20th	Night	22% 14% 34% 24% 5% 1	1050
	21st to end	Night	27% 12% 32% 24% 4	1155

Page generated at 2026-03-30 01:18:42. Version ac07

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